Defining Zero Energy Buildings from a Cradle to Cradle Approach

Several bodies including the DOE, ASHRAE and the IEA SHC Task 40 are working on developing definitions for Net Zero Energy Buildings (NZEBs). Most existing definitions are based on setting a performance metric (quantity and quality) such as site energy, source energy, energy costs, or emissions, and a boundary for the energy source. However, the problem of most existing definitions is that they neglect the energy use during the whole building lifecycle, neglect the climatic context, neglect the urban or city scale, derive from a ‘zero’ or neutralizing notion, link the energy use to area separately from occupants and do not specify the intended definition audience they address e.g. policymakers or building developers or construction professionals. On the other hand, the cradle to cradle approach encourages the creation of ecologically positive footprint buildings where buildings are very efficient by design and by using suitable technologies to become energy positive. The cradle to cradle approach allows us to examine broader criteria including the embodied energy, environmental impact, energy storage and the management of plus energy. Therefore, in this paper, we discuss those problems and suggest a necessary shift to approach NZEB definition, from a cradle to cradle approach rather from a balance approach. This paper provides an overview of existing definitions and compares their impact toward cradle to cradle NZEBs. Finally, the paper sets three principles for defining NZEBs and suggests a definition, metric and calculation method from a cradle to cradle approach